Polarization is a property of waves that describes the orientation of their oscillations. Electromagnetic waves such as light, exhibit polarization. Light whose electric field oscillates in a particular way is said to be polarized. If the oscillation is in a plane, the light is said to be plane polarized. A plane wave, which is a good approximation of most nature light waves, can be polarized in different directions while the plane waves of any polarization can be described by combining any two orthogonally polarized components in P-polarization direction and S-polarization direction. Thus, by the use of a polarizer, it is able to allow one of the two polarized component to pass therethrough while enabling another polarized component to be blocked.
The polarized light had already been vastly applied in our daily life, such as anti-glare illuminants, projectors and displaying devices. Taking a common anti-glare table lamp currently available on the market for instance, there is a multiplayer optical film configured in the table lamp for eliminating polarized glare from a fluorescent lamp with an optical efficiency of about 50%˜60%. Nevertheless, in other applications such as the polarizer in liquid crystal display whose light emission shown to be highly polarized, their optical efficiency can only reach about 40%.
Facing an unavoidable energy shortage crisis, the issues relating to environmental protection and energy saving are becoming the focal point of today's industrial technology research and development. Accordingly, apart from the replacing of the light sources of most currently available illuminations with more energy-efficient light emitting diode (LED), the illumination manufacturers also are striving to construct luminaries with higher optical efficiency. However, since it is known that 50% of nature light can be considered to be the P-polarized light while another 50% to be S-polarized light, the luminaries with conventional absorptive polarizers can easily cause a waste of energy of more than 50%. Thus, to improve the efficiency of polarizer is the key issue both in optical efficiency improvement and in energy saving.
Conventionally, the methods for polarizing the light emitted from a light emitting diode (LED) can be divided into two categories, which are (1) methods for installing polarizers on LED chips; and (2) methods for configuring polarizers into LED package.
One of which is a technique disclosed in U.S. Pat. Pub. No. 20060091412, entitled “Polarized LED”, which relates to a method for installing a reflective polarizer on an LED chip. In the aforesaid disclosure, a reflective polarizer is provided at the LED chip's emitting surface, so that the P-polarization component of the light emitting from the LED chip can travel passing through the reflective polarizer while reflecting the S-polarization component back into the LED chip. It is noted that the S-polarization component being reflected back into the LED chip will first travel passing a quarter-wave plate and then further being reflected back to the same quarter-wave plate, so that the S-polarization component is converted into P-polarization component and is capable of traveling passing the reflective polarizer. With the aforesaid light recycling mechanism, although the efficiency of the LED chip is improved, the luminous output and brightness of the LED chip can be adversely affected since the S-polarization component is reflected back into the LED chip for conversion where it can be absorbed during the process.
Another related technique is disclosed in U.S. Pat. No. 7,495,375, entitled “Polarized light emitting device”, which provides a method for configuring polarizers on the light emitting surface of an LED package. In the aforesaid disclosure, an LED chip is disposed inside a cup-shaped reflector whereas the cup-shaped reflector is filled with a fluorescent material and is covered by a polarizer arranged at the opening thereof. Thereby, light emitted from the LED chip is reflected by the cup-shaped reflector and back into the fluorescent material and the LED chip before it is emitted out through the polarizer from the opening. However, the luminous output and brightness of the LED chip can also be adversely affected since there might be a portion of light being absorbed during the reflection process.
One another related technique is disclosed in TW Pat. No. M287408, which provides a method for forming a polarization layer on the surface of an LED chip or LED package. It is noted that the polarization layer can be formed by a means of adhering or coating. However, since the layer or coating is formed by absorptive polarization material, it can easily cause a waste of energy of more than 50%.
Therefore, it is in need of a light emitting diode (LED) device capable of recycling the beam reflected therein for polarization and thus improving the overall energy efficiency and brightness of the polarized light emitting diode (LED) device.